Historically, exterior door locks have been developed as security devices to make forced entry through a locked door as difficult as possible. This same basic concept has been carried over into the design for interior door locks, although the requirements for the two are obviously distinct, especially from a security standpoint. For all intents and purposes, interior doors require little more than a simple latching device to maintain a door closed against unintentional opening, as by a draft of air. Possible exception to this is found in locks used on doors for bathrooms, bedrooms and dressing rooms where a measured degree of privacy and security is desired.
Because of basic adherence to exterior door lock design, heretofore known interior door latches and locks have exhibited serious disadvantages, especially in their inability to be unlocked quickly if broken or jammed or in emergency situations. As a result, it is all too common for individuals to lock themselves in a room, making emergency entry through the locked door necessary. In order to alleviate this problem, some manufacturers have provided special implements or tools whereby emergency opening of the door lock may be effected. In panic situations, however, those emergency entry provisions are often too time consuming or fail entirely.